Kinetics of the reactions of vinyl (C2H3) and propargyl (C3H3) radicals with NO2 in the temperature range 220-340 K

The kinetics of the reactions of vinyl (C2H3) and propargyl (C3H3) radicals with NO, have been studied in direct measurements at temperatures between 220 and 340 K, using a tubular flow reactor coupled to a photoionization mass spectrometer. The vinyl and propargyl radicals have been homogeneously generated at 193 nm by the pulsed laser photolysis of methyl vinyl ketone (vinyl bromide) and propargyl chloride, respectively. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of NO2 being in large excess over radical concentrations. The bimolecular rate coefficients of both reactions are independent of the bath gas (He or N-2) and pressure within the experimental range (1-7 Torr) and are found to depend on temperature as follows: k(C2H3 + NO2) = [(4.19 +/- 0.05) x 10(-11)](T/300 K)(-060 +/- 0.07) cm(3) molecule(-1) s(-1) and k(C3H3 + NO2) = [(2.55 +/- 0.05) x 10(-11)](T/300 K)(-1.06 +/- 0.10) cm(3) molecule(-1) s(-1), with the uncertainties given as 1 standard deviation. The photolysis of propargyl chloride has also been observed to produce C3H3Cl2 radicals rapidly under the experimental conditions, thus enabling us to measure the bimolecular reaction rate coefficient of the C3H3Cl2 radical with NO2 at room temperature: k(C3H3Cl2 + NO2) = (2.37 +/- 0.05) x 10(-11) cm(3) molecule(-1) s(-1). Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are about +/-20%. The only reaction product observed for the vinyl radical reaction with NO2 is NO. The experimental findings have been compared with the results of ab initio calculations, which give insight into possible reaction pathways.